Personally, I'm VERY happy that Qt collection sizes are signed. It seems
nuts to me that an integer value potentially used in an expression using
_subtraction_ be unsigned (e.g. size_t).
An integer being unsigned doesn't guarantee that an expression involving
that integer will never be negative. It only guarantees that the result
will be an absolute disaster.
$0.02
- Phil W.
On 9/3/2013 12:58 PM, Constantin Makshin wrote:
> Thanks for the explanation, although I still don't appreciate the choice
> (mostly regarding the size, not signedness). :)
>
> On 09/03/2013 10:48 PM, Thiago Macieira wrote:
>> On terça-feira, 3 de setembro de 2013 22:18:39, Constantin Makshin wrote:
>>> Could you please explain (or give a link to an article or something like
>>> that) the reasons Qt developers used to choose signed 32-bit integer for
>>> this purpose?
>>> Signed 32-bit container sizes, i.e. number of elements in a container,
>>> would be acceptable (considering the equation 'n * sizeof(T)' for the
>>> amount of memory consumed by the array alone) but why use them to
>>> calculate and store sizes of allocated memory blocks?
>> For two reasons:
>>
>> 1) it's signed because we need negative values in several places in the API:
>> indexOf() returns -1 to indicate a value not found; many of the "from"
>> parameters can take negative values to indicate counting from the end. So
>> even
>> if we used 64-bit integers, we'd need the signed version of it. That's the
>> POSIX ssize_t or the Qt qintptr.
>>
>> This also avoids sign-change warnings when you implicitly convert unsigneds
>> to
>> signed:
>> -1 + size_t_variable => warning
>> size_t_variable - 1 => no warning
>>
>> 2) it's simply "int" to avoid conversion warnings or ugly code related to the
>> use of integers larger than int.
>>
>> io/qfilesystemiterator_unix.cpp:
>> size_t maxPathName = ::pathconf(nativePath.constData(),
>> _PC_NAME_MAX);
>> if (maxPathName == size_t(-1))
>>
>> io/qfsfileengine.cpp:
>> if (len< 0 || len != qint64(size_t(len))) {
>>
>> io/qiodevice.cpp:
>> qint64 QIODevice::bytesToWrite() const
>> {
>> return qint64(0);
>> }
>>
>> return readSoFar ? readSoFar : qint64(-1);
>>
>>
>>> On 09/03/2013 08:42 PM, Thiago Macieira wrote:
>>>> On terça-feira, 3 de setembro de 2013 19:33:47, Mehmet İpek wrote:
>>>>> Btw, size
>>>>> limit of QVector is 2^31 in 64 bit platforms too?
>>>> Yes. All Qt container classes use a signed int for sizes.
>
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